Until very recently the DVD copy-protection community considered watermark-detection for playback-control in a personal computer to take place in the DVD-ROM or DVD-rewriter drive. The motivation for this position was that watermark-detection is a permissive technology (i.e. the playback or recording device works with or without watermark detector) as opposed to encryption, which requires a decryptor for the device to function properly. The fragile consensus used to be that DVD-ROM drives would inspect MPEG2-compressed unencrypted DVD-video content on disks for presence of a copy-never or copy-once watermark. If such were the case, playback should be stopped (because copy-once or copy-never content should be encrypted at all times).
FIG. 1 shows schematically such a PC system architecture with watermark-detection for playback-control in the DVD-drive. The PC comprises a DVD-drive 1, a motherboard 2 with microprocessor and associated circuitry for executing the operating system and application software, and a graphics card 3. The motherboard is provided with an IDE-bus 4 for transferring data to and from the DVD-drive, and an AGP-slot or PCI-slot 5 for connecting the graphics card. The DVD-drive includes a basic engine 11 for reading data from a DVD disk 6 and a host interface 12 for connecting the drive to the IDE bus. In order to enable watermark detection by a watermark detector core 14, the drive comprises an MPEG2-parser 13 to at least partially decompress the content. Stopping playback of content is symbolically denoted by means of a switch 15, which is controlled by the watermark detector core 14.
However, a PC system with playback-control using a watermark detector in the DVD drive leaves major security holes in an open-architecture PC. One such security hole is that content may be recorded in scrambled form by flipping all bits. Since this is no longer a compliant MPEG2 stream, the parser 13 in the drive will fail and no watermark will be seen. The bit-flip can be undone just before or inside the media-player software. Another such security hole is that content may be compressed not using MPEG2, but using other compression schemes such as MPEG4 (popularized under the name DivX), fractal coding, Windows Media, Real, etc. Since it is impossible for the DVD-drive to have parsers on board for all of these formats (and hackers will invent new codecs to outsmart the drive), the watermark will not be detected. Although (illegal) copies compressed with a codec other than MPEG2 will generally not play on current DVD-video players there is a trend for DVD-video players to support more and more codecs.
Therefore it has already been proposed to place the watermark detector after decompression and just before rendering, i.e. in an MPEG-decoder card or in a graphics card. After decompression there is no longer confusion because all content reduces to the unequivocal baseband-format ready for consumption by human eyes. Initially, it was considered difficult to enforce MPEG-decoder companies or graphics-card manufacturers to install such watermark detectors. This perception has changed since.
Although it is architecturally very simple and clean to detect watermarks in the graphics-card, in practice there are a number of problems with this location, due to the enormous amounts of data that flow through the graphics card at huge speed, and due to the fact that multiple streams can be displayed at the same time.